Conventionally, development of an exhaust device with a purpose of improving the torque has been conducted for multicylinder engines mounted to an automobile or the like.
For example, Patent Document 1 discloses a technique in which exhaust passages of cylinders that are non-sequential in exhaust order are bundled and converged as a tapered exhaust pipe, and an ejector effect is provided in this narrowed portion to prevent exhaust interference between the cylinders.
Patent Document 1: Japanese Patent Application Laid-open No. H04-036023 (page 4, page 5, and FIG. 3)